Staff there told me before the work load can be quite heavy as each officer has numerous payment companies under their supervision (you will be the main contact person for all matters relating to the companies assigned to you, be it questions from the company itself, other departments, bosses, members of public and so on).

Not clear what you mean by operate like fintech. MAS being part of public service, you will have to clear most or all matters (even fairly straightforward outgoing emails) relating to your supervised companies through at least one layer (your team leader), if not two (your division head) or more (department head and above). While I haven’t heard anything very bad about the bosses there, some will find the clearance process a chore as you will find some MAS bosses give a large amount of attention to writing - even for pieces of work that are relatively low on the scale of importance (not intended for public consumption, does not require clearance beyond team leader or division head). It is fair to say the iterative process of rewriting output can consume a large amount of officers time depending on who you get to work with.

As with any job offer, ultimately you have to assess for yourself whether your perception of the “brand name” and learning experience you hope to receive, balanced against other cons of the job that are not apparent before joining, is worth the package offered.